Layered double hydroxides (LDH) of Mg and Al and their corresponding layered mixed metal oxides (LDO) are promising sorbents for CO2 capture. Because of their compositional flexibility and structural complexity, they possess energetically different basic sites. We have investigated the energetics of CO2 uptake by measuring enthalpy of CO2 adsorption of the [Mg-Al-CO3] LDH and LDO of two different compositions (Mg/Al = 2:1 and 3:1). The initial adsorption enthalpies for all the LDH and LDO are similar, indicating that the available sites are similar for initial uptake. However they vary substantially with increasing coverage depending on the nature and number of basic sites available for adsorption. This difference could possibly be related to the presence of interlayer in the LDHs and its absence in LDOs. Initial adsorption in both the cases happens on the surface, while with increasing coverage in LDHs, adsorption proceeds on the interlayer and is associated with more exothermic adsorption enthalpy. Attenuated total reflectance (ATR) measurements of samples after CO2 uptake, aids in identifying the mode of binding of adsorbed carbonate, which gives insights on nature of binding and strength of basic sites which supplements the data obtained by adsorption calorimetry. LDHs and LDOs of composition 2:1 and 3:1 prepared by Riechle method show similar CO2 uptake characteristics with minor differences whereas the sample prepared by urea hydrolysis exhibits poor CO2 uptake owing to its high crystallinity and low surface area.

Energetics of CO2 adsorption on Mg-Al layered double hydroxides and related mixed metal oxides

249th National Meeting (2015)

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